Conventional aircraft consist essentially of a wing section and a fuselage. This so-called “tube and wing” configuration enables convenient packaging of passengers and cargo, but has certain drawbacks. In most cases, passengers are seated on a deck disposed approximately on the vertical centerline of the fuselage, while cargo is stowed beneath. This enables a relatively wide, flat floor for seats and separates cargo operations from passenger loading and unloading. Passengers can be loaded via one or more passenger doors, while cargo can be loaded from one or more cargo hatches on the underside or sides of the fuselage. This configuration also provides a relative constant fuselage cross section (less the nose and tail cones), enabling a substantially percentage of the available volume of the fuselage to be utilized.
While convenient from a packaging standpoint, the tube and wing configuration is not particularly efficient. This is because the fuselage provides little or no lift, yet introduces substantial drag. Thus, the wing must provide substantially all of the lift required for the aircraft to fly. This configuration requires a wing that is larger, thicker, and/or more cambered than would otherwise be required (i.e., if the fuselage provided a larger percentage of the required lift). This results in a wing with higher lift, but proportionately higher drag. Thus, the engines must provide enough thrust to overcome the drag from both the fuselage and the (now higher drag) wing.
In a blended wing configuration, on the other hand, both the fuselage and the wing provide lift. As the name implies, the blended wing blends the wing and fuselage together to provide a single, lift-producing body. In this configuration, the fuselage serves to both carry passengers and/or cargo and to provide a significant portion of the lift. As a result, the wing portion can be smaller for a given payload. Thus, blended wing aircraft tend to have significantly lower overall drag and can carry larger payloads while consuming less fuel.
Due to their unconventional shape, however, blended wing aircraft can present some challenges with regard to packaging. In other words, because the shape of the fuselage is more irregular than a conventional tube-shaped fuselage, providing storage for cargo, equipment, passengers, and other components can be challenging. In particular, as shown in FIGS. 1A and 1B, finding a suitable place to stow the retracted landing gear 105 can be challenging. In general, it is desirable to place the main, or rear, landing gear 105a fairly close to the center of gravity, CG, of the aircraft. This placement reduces the aerodynamic forces that must be generated by the flight control surfaces 120 (e.g., elevons 110 and/or flaps 115) to rotate the aircraft on take-off. In other words, if the main landing gear 105a is placed too far from the CG, the flight surfaces cannot overcome the weight of the aircraft acting on such a large lever arm, LMG, for the purposes of takeoff rotation.
As shown in FIG. 1A, therefore, from a weights and balances standpoint, it is desirable to place the main gear 105a as close to the CG as possible. In addition, the maximum width, or track, of the landing gear is limited by regulation to ensure landing gear/runway compatibility. In a blended wing design, however, this unfortunately places the landing gear in the middle of the desired passenger compartment (on a single level aircraft) or in the middle of the cargo compartment (on a multi-level aircraft). This reduces seating and/or cargo capacity and makes packaging, interior aesthetics, and utility more difficult, among other things.
As shown in FIGS. 2A and 2B, one solution is to simply move the main landing gear 105a rearward out of the passenger compartment 125. Unfortunately, this places the main landing gear 105a at a substantial distance from the CG. This, in turn, creates a large lever arm LMG, between the CG and the contact patch of the main landing gear 105a. In this configuration, the elevons 110 and/or flaps 115 are likely unable to generate enough negative lift at the rear of the wing to rotate the plane for takeoff. Thus, one problem—clearing the passenger and/or cargo compartment—has been traded for another—increasing takeoff distance or not being able to take off at all. Of the two, taking off is clearly more important in an aircraft.
What is needed, therefore, is a system and method for rotating the aircraft for takeoff using something other than the aerodynamic control surfaces. After takeoff, the location of the main landing gear 105a is relevant only to the overall weights and balances of the plane (e.g., center of lift, CL vs CG). The system should be simple and robust and provide pilots with a similar tactile experience as a conventional configuration. It is to such systems and methods to which examples of the present disclosure are primarily directed.